Place a vibrating tuning fork (usually 128 c/s) on a bony prominence, e.g. radius. Ask the patient to indicate when the vibration, if felt, ceases. If impaired, move more proximally and repeat. Vibration testing is of value in the early detection of demyelinating disease and peripheral neuropathy, but otherwise is of limited benefit.
If the above sensory functions are normal and a cortical lesion is suspected, it is useful to test for the following:
Two point discrimination: the ability to discriminate two blunt points when simultaneously applied to the finger, 5 mm apart (cf, 4 cm in the legs). Sensory inattention (perceptual rivalry): the ability to detect stimuli (pin prick or touch) in both limbs, when applied to both limbs simultaneously.
Stereognosis: the ability to recognise objects placed in the hand. Graphaesthesia: the ability to recognise numbers or letters traced out on the palm.
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